Many thanks to those of you who sent information on prices you paid
for your textbooks. I've compiled all the data received so far, and
deleted non-physics books, introductory books, and paperback books.
This left 49 data points, all upper-division or graduate texts.
I then adjusted each price to 1997 dollars based on the consumer
price index (http://146.142.4.24/cgi-bin/surveymost?cu), and found
a rather striking, if preliminary, result: In constant dollars,
textbook prices did not change significantly between 1960 and 1984.
The average price of such a book during these years was about $52
(1997 dollars), with a standard deviation of $12.
I could still use more data, especially from after 1965, to see if
there were any significant trends during this time interval. I could
also use some data from the late 80's and early 90's. It's easy to
get data for the present, from Amazon.com or my local bookstore.
Depending on the exact sample used, I suspect that that the average
price today would come to about $70 or a little more. My tentative
conclusion is that after adjusting for inflation, textbook prices
have risen about 30 or 40 percent, and that this increase has occurred
entirely since 1984.